Paper making wire cloth

ABSTRACT

The invention relates to a paper making wire cloth, especially for the sheet forming zone, comprising a paper side ( 12 ) and a backing side ( 14 ). Said wire cloth is formed out of at least one type of transverse threads ( 16, 18 ) which are interwoven with at least one type of longitudinal threads ( 20 ), said threads together forming repeats (A-H) and at least two different types of intersection ( 22, 24 ). The longitudinal threads ( 20 ) are alternated within the respective repeat (A-H) on the backing side ( 14 ), forming the other type of intersection ( 24 ); and the transverse threads ( 18 ) on the backing side ( 14 ) are held on their outer side ( 26 ) which faces the paper side ( 12 ), by at least two longitudinal threads ( 20 ) within said repeat (A-H) on the backing side ( 14 ). Maximum fibre support is thereby achieved on the paper side accompanied by little marking of the upper side as the points of alternation or intersections are evenly distributed.

[0001] The invention relates to a paper making wire cloth, for the sheetforming zone in particular, with a paper and a backing side, a wirecloth made up of at least one type of cross-thread and at least one typeof lengthwise thread interwoven with the former, which threads togetherform at least two different types of crossings, the weave pattern madeup of the lengthwise and cross-threads of the paper side being repeatedbetween crossings of the same kind and the lengthwise threadsalternating from the backing side to the paper side and conversely toform the respective other type of crossing.

[0002] A growing number of high-performance papermaking machines withspeeds of up to 2000 meters per minute and working widths above 10meters are used in the paper production industry today. The sheetforming unit is very generally designed as a double cloth former, and inmany cases as a split former. It is typical of the machines that thesheet forming process takes place immediately between two paper makingwire cloths in a relatively short drainage zone. The time required forsheet formation is reduced to milliseconds by this short distance andthe high production rate. Over this interval the solid fraction or drycontent of the fiber suspension must be increased from about 1 percentto about 20 percent. For the papermaking wire cloth this means that thismachine must be characterized by very high drainage performance and yetleave no markings in the paper and must also provide high fiber support.

[0003] Another important point is the transverse stability of wire clothtension; this stability is of decisive importance in determining thethickness and moisture profile of the sheet. Very strict requirementsare set in this connection precisely for modern machines characterizedby large operating widths. In order to improve sheet formation, shapingstrips are consequently used with increasing frequency in the sheetforming zone; they are mounted alternately on the backing sides of thewire cloth and are pressed against these sides. The result is rapidlyalternating load deflection of the cover of the wire cloths in thelongitudinal direction.

[0004] Today an effort is customarily made to meet these requirements byuse of composite fabrics. A composite fabric used for this purpose isdescribed in DE 42 29 828 C2, for example. The conventional papermakingwire cloth in question consists of two superposed wire cloth fabrics inthe form of single layers which are interconnected by binding threadsextending in the cross and/or lengthwise direction, one of the fabricsbeing in the form of definition fabric having the mechanical propertiesof the composite fabric with respect to extension and the other wirecloth fabric in the form of reaction fabric of higher tension and lowerrigidity than the definition fabric. The wire cloth fabrics in questionthus consist of warp threads and woof threads, these threads beingconnected to each other by additional binding threads. As a result ofthe design of the cloth fabrics as reaction or definition fabrics,internal wear, especially wear of the binding threads, is resisted andin this way the service life of the combination fabric is lengthened andundesirable separation of the wire cloth fabric layer is prevented overa long period. The internal wear in question of a combination fabric iscaused especially by the circumstance that, during redirection of thewire cloth such as occurs in the area of guiding rollers of the wirecloth batch by way of which the combination fabric is guided, theindividual wire cloth fabric layers are stretched or crushed to varyingdegrees.

[0005] Since the binding threads in question not only belong to thestructure of the fabric but are independent components, they are kept assmall as possible in diameter in order to disrupt drainage as little aspossible. But with correspondingly high stresses the possibility thenexists that the thin binding threads will then break and the connectionbetween the wire cloth fabrics will be interrupted. In the case of ageneric papermaking wire cloth as disclosed in EP 0 432 413 B1, whichalso has the structure of a composite fabric, while the proposal hasalready been made that binding threads be used as two fabric-specificthreads and interlaced with the other fabric layer involved to formx-shaped crossings in order to prevent the disadvantages in the state ofthe art described, the accumulation alone of the known change points inthe cross-direction also results unintentionally in stiffening of theconventional fabric. Considerable differences in length may occurespecially over greater weaving lengths which, in turn, are manifestedin difference in tension, with the result that fabric-specific bindingthreads break and may result in failure of the conventional papermakingwire cloth. It is also known in connection with this conventionalspecial type of weave that it is more or less possible to produce onlycross-threads of one kind, that is, cross-threads of more or less thesame diameter, for both the upper and the lower fabric, something whichreduces the possibility of efficient support on the backing side. Inaddition, manufacture of the conventional interlocking fabric is costly.

[0006] On the basis of this state of the art the invention has theobject of further improving papermaking wire cloths of the type referredto with the aim of making a longer service life available in papermakingand of making the process more cost-effective. An object as formulatedin these terms is attained by the papermaking wire cloth having thecharacteristics specified in claim 1.

[0007] In that, as specified in the descriptive portion of claim 1,replacement of the lengthwise threads is accompanied by formation of theother type of crossing within this repeat of the backing side, and inthat the cross- threads of the backing side are held by at a minimum oftwo lengthwise threads within this repeat of the backing side on itsouter side facing away from the paper side, maximum fiber support isachieved on the paper side, along with only slight marking of the upperside, since uniform distribution of the alternating or crossing pointsis achieved. Since layer binding in the lengthwise direction by allthreads is present, unintentional layer separation is also preventedwith high certainty.

[0008] As a result of support on the external side by way of at leasttwo lengthwise threads of a repeat, it is additionally possible toselect cross-threads for the backing side which are thicker than thecross-threads of the paper side and yet to ensure reliable support bythese threads in the papermaking wire cloth. As a result, the supportforces may be usefully increased and the drainage output correspondinglyincreased by means of the relatively “open” backing side formed in thismanner. Preferably a woof ratio of 2:1 is to be chosen. In addition, theoperating time potential for the papermaking wire cloth is maximized bythe long-floating backing side with its wefts widened in cross-sectionand high lateral stability is nevertheless achieved on the basis of thetwo separated woof layers.

[0009] Other advantageous embodiments are specified in the dependentclaims.

[0010] In what follows the papermaking wire cloth claimed for theinvention is described in detail on the basis of one embodiment. Indiagrammatic form and not to scale,

[0011]FIG. 1 shows a portion of a side view of the papermaking wirecloth claimed for the invention;

[0012]FIG. 2 a top view of the backing side of the wire cloth shown inFIG. 1, along line 1-1;

[0013]FIG. 3 a bottom view of the backing side of the papermaking wirecloth shown in FIG. 1.

[0014] The figures show in part a wire cloth fabric identified as awhole as 10 for a papermaking wire cloth not shown as a whole, which maybe used in particular for the so-called sheet forming zone in the caseof conventional papermaking machines. The wire cloth 10 has a paper side12 and a backing side 14. The paper side 12 and backing side 14 inquestion are made up of two different types of cross-threads 16, 18 andat least one type of lengthwise thread 20 interwoven with them. Thecross-threads 16, 18 form, with the lengthwise threads 20 interwovenwith them, in both the lengthwise and the cross directions, as viewed inthe line of vision to the wire cloth fabric 10, eight-shank repeats A toH which are repeated correspondingly in the lengthwise and the crossdirections. Two different types of x-shaped crossings 22, 24 are formedwithin the wire cloth fabric 10 during formation of the repeats A to Hin question (see FIG. 1). As is to be seen in FIG. 1, one lengthwisethread 20 of the same type extends at a crossing 22 of the same type inone direction, for example, with positive pitch, and with negative pitchat the crossing of the other type, 24 in this instance.

[0015] As the figures also show, the weave pattern made up of thelengthwise threads 20 and cross-threads 16 of the paper side 12 isrepeated between crossings 22 of the same type, the lengthwise threads20 alternating from the backing side 14 to the paper side 12 and viceversa between the two crossings 22 of the same type and form therespective other type of crossings 24. Consequently, it is claimed forthe invention that alternation of the lengthwise threads 20, in contrastwith the state of the art, takes place within the particular repeat A toH of the backing side 14 to form the other type at crossings 24. Inaddition, as is to be seen especially in FIG. 3, the cross-threads 18 ofthe backing side 14 are held by at least two lengthwise threads 20within this repeat A to H of the backing side on its outer side 26facing away from the paper side 12. The weave in question claimed forthe invention makes it possible to double the number of woofs on thepaper side 12 relative to the backing side 14 shown. A woof ratio of 2:1is accordingly obtained between paper side 12 and backing side 14, whilea woof ratio of only 1:1 is generally obtained with the conventionalsolutions.

[0016] The thread diameters which can thus be incorporated on thebacking side 14 may in this way be doubled in cross-section relative tothe paper side 16. This in turn means that the volume of the materialundergoing wear (ground), and accordingly the service life of the wirecloth claimed for the invention, may be increased considerably both bythe long-floating weave and the greater diameter on the backing side 14.In addition, as a result of “open” backing side achieved, thepermeability of the wire cloth fabric 10 is increased and so thedrainage properties are distinctly improved. Since in the case of thepapermaking wire cloth claimed for the invention all connectinglengthwise threads 20 are arranged in direct sequence, in contrast withthe conventional fabric solutions there is no interposed face weft orface warp, so that the wire cloth fabric 10 claimed for the inventionhas a connection pattern largely homogenous in form and a reliableconnection acting equally in each direction of the fabric is obtained.The weave pattern of the paper side 12 consists of a conventional linenweave which extends between crossings of one kind 22 and the immediatelyfollowing other kind 24, which is of eight-shank configuration.Provision is also made such that the backing side 14 with each repeat Ato H is of eight-shank configuration as viewed in both directions.

[0017] The respective lengthwise threads 20, which support thecross-threads 18 of the backing side 14 on its outer side 26 facing awayfrom the paper side 12, are mounted so as to be adjacent to each otherat least once in pairs (see FIG. 3). It has been found to be especiallyadvantageous from the viewpoint of production technology for thecross-threads 16, 18 to be in the form of woof threads and thelengthwise threads 20 in that of warp threads. As is to be seen in FIG.1 in particular, the crossings of one type 22 are supported on thebacking side 14 by two cross-threads 18 and the crossing of the othertype 24 by four cross-threads 18 as viewed in the direction of thebacking side 14, these supporting cross-threads 18 being positioned moreor less in one common plane on the outer side 26 of the backing side 14.

[0018] In addition, the respective lengthwise threads 20 which adjointhe cross-threads 18 of the backing side 14 on their side facing thepaper side 28 (see FIG. 2) are grouped in pairs side by side; up tothree groups may be joined immediately adjacent to each other within arepeat A to H (see cross-thread 18D in FIG. 2). A different, regularlyrepeated, weave pattern is also conceivable in this instance in place ofthe linen weave on the paper side 12. As a result of the equivalentbonding of paper side 12 and backing side 14, a unified texture isprovided rather than, as in the state of the art, a composite fabricmade up of individual fabrics separable from each other. The papermakingwire cloth is nevertheless multilayered in structure and could becorrespondingly augmented to produce a composite fabric.

1. A papermaking wire cloth, for the sheet forming zone in particular,with a paper (12) and a backing (14) side, made up of at least one typeof cross-thread (16, 18) and at least one type of lengthwise thread (20)interwoven with these cross-threads (16, 18), which lengthwise threads,which together make up at least two different types of crossings (22,24) while forming repeats (A-H), the weave pattern made up of thelengthwise (20) and cross (16) threads of the paper side (12) beingrepeated between crossings (22) of the same type, and the lengthwisethreads (20) alternating between the two crossings (22, 24) of the samekind from the backing side (14) to the paper side (12), and vice versa,and the respective other type of crossing (24) being formed,characterized in that alternation of the lengthwise threads (20)accompanied by formation of the other type of crossings (24) takes placewithin the respective repeat (A-H) of the backing side (14) and in thatthe cross-threads (18) of the backing side (14) are held within thisrepeat (A-H) of the backing side, on its outer side (26) facing awayfrom the paper side (12), by at least two lengthwise threads (20). 2.The papermaking wire cloth as claimed in claim 1, wherein the weavepattern of the paper side (12) consists of a linen weave.
 3. Thepapermaking wire cloth as claimed in claim 2, wherein the linen weavewhich extends between the crossings of one type (22) and of theimmediately following other type (24) is made up of eight shanks.
 4. Thepapermaking wire cloth as claimed in claim 1 or 2, wherein the backingside (14) within each repeat (A-H) is made up of 8 shanks.
 5. Thepapermaking wire cloth as claimed in one of claims 1 to 4, wherein therespective lengthwise threads (20) which support the cross-threads (18)of the backing side (14) on its outer side facing away from the paperside (12) are positioned at least once in pairs, one adjacent to theother.
 6. The papermaking wire cloth as claimed in one of claims 1 to 5,wherein the cross-threads (18) of the backing side (14) are larger incross-section than the cross-section of the cross-threads (16) of thepaper side (12).
 7. The papermaking wire cloth as claimed in claims 1 to6, wherein the cross-threads (16, 18) are in the form of woof threadsand the lengthwise threads (20) in the form of warp threads.
 8. Thepapermaking wire cloth as claimed in one of claims 1 to 7, wherein therespective crossing (22, 24) is in the form of an x.
 9. The papermakingwire cloth as claimed in one of claims 1 to 8, wherein the crossings ofone type (22) are supported on the backing side (14) by twocross-threads (18) and the crossing of the other type (24) by fourcross-threads, and wherein these supporting cross-threads (18) arepositioned in a common plane on the outer side (26) of the backing side(14).
 10. The papermaking wire cloth as claimed in one of claims 5 to 9,wherein the respective lengthwise threads (20) which delimit thecross-threads (18) of the backing side (14) on its side (28) facing awayfrom the paper side (12) are present in up to three groups, thecross-threads (18) being grouped in pairs, one thread next to the other.